A critical consideration in the production of fluid hydrocarbons from marine deposits lies in providing a fluid communication system from the marine bottom to the surface after production has been established. Such a system, commonly called a production riser, usually includes multiple conduits through which various produced fluids are transported to and from the surface, including oil and gas production lines, service, electrical and hydraulic control lines.
For offshore production, a floating facility can be used as a production and/or storage platform. Since the facility is constantly exposed to surface and sub-surface conditions, it undergoes a variety of movements. In such a zone of turbulence, heave, roll, pitch, drift, etc., may be caused by surface and near surface conditions. In order for a production riser system to function adequately with such a facility, it must be sufficiently compliant to compensate for such movements over long periods of operation without failure.
Examples of such compliant marine riser systems are disclosed and discussed in U.S. Pat. Nos. 4,182,584; 4,367,055; 4,400,109; and 4,423,984; in paper OTC 4512, "Deepwater Production Riser", Panicker and Yancey, presented at the 15th annual Offshore Technology Conference, Houston, Tex., May 2-5, 1983; and in co-pending U.S. patent application Ser. No. 722,026, filed concurrently herewith. As seen from these references, a typical compliant riser system includes (1) a vertically rigid section which extends from the marine bottom to a fixed position below the zone of turbulence that exists near the surface of the water, and (2) a flexible section which is comprised of flexible flowlines that extend from the top of the rigid section, through the turbulent zone, to a floating vessel on the surface. A submerged buoy is attached to the top of the rigid section to maintain the rigid section in a substantially vertical position within the water.
Due to the substantial water depths in those production areas where compliant or equivalent marine risers are designed for use, the use of divers on or near the marine bottom is viturally prohibited. Accordingly, the lower end of the marine riser must be capable of being remotely connected to the marine bottom without requiring any substantial assistance from divers. To accomplish this in most previously known systems of this type, a hydraulic connector is attached to the lower end of the riser and long flowlines are extended from the surface to supply the hydraulic fluid required to actuate the connector. The deployment and handling of these long flowlines can present substantial problems especially in rough waters.
Further, the hydraulic connector is normally a separate unit which is bolted or otherwise secured to the lower end of the riser. As such, the point at which the connector is joined to the riser is subjected to substantial forces when the riser experiences forces which tend to move the riser to and from vertical about a pivot point inherently existing at the lower end of the riser where it is secured to the marine bottom. Continued application and relaxation of these forces can lead to failure at the "weakened" point where the separate connector is joined to the riser.
Further, since risers of this type may have to be removed and/or replaced during or at the end of their operational lives, the connector used for connecting a riser to the marine bottom should also be capable of being remotely released.